The demand for weight reduction in e.g. the automotive industry has led to the development and implementation of lightweight materials, and related manufacturing processes and tools. The growing concern for occupant safety also leads to the adoption of materials which improve the integrity of the vehicle during a crash while also improving the energy absorption.
In that sense, vehicle parts made of high-strength and ultra-high-strength steel (UHSS) are often employed in order to satisfy criteria for lightweight construction.
A process known as Hot Forming Die Quenching (HFDQ) uses boron steel sheets to create stamped components with ultra-high-strength steel properties, with tensile strengths of e.g. 1,500 MPa or 2,000 MPa or even more. The increase in strength allows for a thinner gauge material to be used, which results in weight savings over conventionally cold stamped mild steel components.
Some of these steels, such as e.g. 22MnB5 steel, are designed to attain a microstructure after heat treatment, which confers good mechanical properties. 22MnB5 is sometimes presented with an aluminum-silicon coating and is known as Usibor® 1500P, commercially available from Arcelor Mittal. It is an example of a steel used in various components, possibly involving so-called tailored and patchwork blanks. Usibor® 1500P is supplied in ferritic-perlitic phase. It is a fine grain structure distributed in a homogenous pattern. The mechanical properties are related to this structure. After heat treatment during a hot forming process, a martensite microstructure is created. As a result, maximum tensile strength and yield strength increase noticeably.
Typical vehicle components that may be manufactured using the HFDQ process include: door beams, bumper beams, cross/side members, NB pillar reinforcements, and waist rail reinforcements.
Simulations performed during the design phase of a typical vehicle component can identify points or zones of the formed component that need reinforcement (because lighter and thinner metal sheets and blanks are used) in order to increase strength and/or stiffness. Alternatively a redesign may be done in order to obtain a desired deformation behaviour.
In that sense, there are several procedures with which some areas of a component can be reinforced or weakened in order to redistribute stress and save weight by reducing the thickness of the component. These known procedures for reinforcing a component are, for example, procedures adding welded reinforcements prior to any forming process. Such reinforcements may be “patchworks” in which partial or complete overlapping of several blanks may be used, or blanks or plates of different thickness that may be welded “edge to edge”, i.e. Tailor welded blanks (TWB). Structural mechanical requirements can thus be achieved theoretically with a minimum of material and thickness, i.e. weight.
In these methods however, further manufacturing processes are involved. Additionally, when ultra-high strength steels are being hot formed some weldability problems may arise due to an aluminum-silicon (AlSi) coating usually used to protect from corrosion and oxidation damage. In order to overcome these problems it is known to remove a part of the coating in an area close to the welding gap by laser ablation. However, this represents yet an additional step in the manufacturing process of a vehicle component.
Furthermore, when welded reinforcements (patchworks) are added to a blank, partial or complete overlapping of blanks occur. These areas are potential corrosion starting points as overlapped regions remain underneath and do not receive e.g. a corrosion coating.
In addition, depending on the component being formed there may be regions in which it is not possible or it is at least cumbersome to use welded reinforcements e.g. corners or areas with elevation changes. Patchworks are normally welded using a spot welding which requires a minimum space to distribute the spots. Additionally, patchworks need a minimum size in order to be easily welded. This may involve an extra weight as the reinforcement needs to have a minimum size in order to be welded rather than having the right size (minimum) needed to reinforce the required area.
Document EP1621439 describes methods of forming a weld type metallic surfacing in a zone on at least one side of a thin metallic structure by laser beam. However, boundary areas of such a metallic surfacing may involve locally lower cooling rates than that at the surfacing area thus resulting in weaker points/zones.
The aforementioned problems and/or challenges are not unique to the automotive industry or to the materials and processes used in that industry. Instead these challenges may be encountered in any industry wherein weight reduction is an objective. When weight reduction is an objective, the components become ever thinner which can thus lead to an increased need for reinforcements.
It is an object of the present disclosure to provide improved methods of manufacturing reinforced structural components.